1) Field of the Invention
The present invention relates to a device and method for braiding fibers into a braided structure, in particular a multilayered braided structure.
2) Description of the Related Art
Such braided structures may be used as such, but are preferably used to form the reinforcing core of a fiber reinforced plastic product. To produce such a product, the braided structure is typically positioned in a mold and a resin is injected into this mold, and subsequently cured. This procedure is used in particular in the case of a fiber reinforced plastic with a high fiber content, typically more than 60% by volume. Fiber reinforced plastic products created in this way combine a high strength with low weight, and are used in aviation and aerospace applications for instance. A further possible use is in automobile construction.
A braided structure is typically manufactured using a system of equipment including a braiding machine, a forming device, including a forming ring, and a take-up device. The braiding machine consists of a track plate, onto which a plurality of yarn carriers is positioned. The yarn carriers carry the spools of yarn and may use tension controls to release the yarn during processing. Half of the yarn carriers are driven in a clockwise direction and half are driven in a counterclockwise direction. The movement of carriers is guided by the track plate that causes the two sets of opposing carriers to travel in a Maypole fashion around carrying yarns that extend perpendicular to the plane of the braiding machines track plate. At the point where the yarns consolidate to form the braid (frequently referred to as the braid point), a forming device is often used to control the dimension and shape of the braided fabric. Traditionally, the forming device comprises a forming ring that controls the outside diameter of the finished braided product. The tension required to pull the yarn off of the carriers and to pull the finished braid is supplied by a take-up device. The take-up device applies the force by pulling on the finished braid.
On account of the lack of inherent stability of a braided structure, the latter is usually braided around a solid mandrel in the shape of the final product to be obtained. The mandrel controls the inside dimensions of the braided product. During the braiding operation, the mandrel and the braiding machine are moved in relation to each other in order to create a sheet like structure. The thickness of the braid may be controlled by varying the thickness of a braided layer or by providing a plurality of layers arranged on top of each other.
During the known braiding process, the braiding machine and forming ring enclose the mandrel, and the mandrel is translated in a more or less linear fashion through the braiding machine and forming ring. In this way, so called 2.5D products can be formed. Such products are linear or curvilinear in shape, but may vary in the lateral dimension along their axis.
There is a need however to be able to produce continuous braided structures. Continuous structures are endless structures, and therefore have no discernable beginning or end. Examples of such structures include frame like structures, such as car chassis body parts. Such frame like structures may have any 3-dimensional (3D) form, and may be doubly curved for instance. The known method of producing such structures is to braid a number of 2D or 2.5D structures, and assemble these to form the desired frame like structure. However, such a method requires the use of separate connecting parts, and is therefore time consuming and expensive. Particularly in the case of fiber reinforced plastic products, the connecting areas moreover represent weak spots in the product.
The object of the invention therefore is to provide a device and method for braiding fibers into a continuous braided structure, which structure does not need to be assembled.